1. Field of the Invention
The present invention relates to a control device for an internal combustion engine of a straddle type vehicle.
2. Description of Related Art
An internal combustion engine using a mixed fuel formed by mixing gasoline and alcohol is known. An engine using the mixed fuel has a problem in that an increase in the mixing ratio of alcohol in the mixed fuel causes deterioration in the warming-up performance of the engine.
In view of the above, JP-B-62-54987 discloses a fuel supply device for improving the warming-up performance of the internal combustion engine. JP-B-62-54987 describes a control for enriching (lowering) an air fuel ratio by reducing the opening of the choke valve when the alcohol concentration is equal to or more than a predetermined value after a complete explosion in a fuel supply device of an engine. The control comprises an alcohol concentration sensor, a choke valve and a carburetor including a complete explosion correcting mechanism for opening the choke valve by a fixed opening after a complete explosion (namely, after a first explosion).
The control described in JP-B-62-54987 is control after the first explosion for the purpose of improving warming-up performance. In an internal combustion engine using mixed fuel, however, the mixed fuel decreases in volatility when the mixing ratio of alcohol is high, which sometimes causes difficulty in achieving an excellent first explosion. That is, there is a problem in that the startability of the internal combustion engine is deteriorated.